This invention relates to a hydraulic autotensioner for keeping constant the tension in a timing belt mounted in an automotive internal combustion engine.
The applicant of this invention proposed an autotensioner of this type as shown in FIGS. 8A, 8B.
This autotensioner comprises a tubular pivot shaft 162 fixed in position by tightening a bolt 161 into an engine block 160, an eccentric ring 163 supported on the pivot shaft 162 at its off-center point, a pulley 164 rotatably supported on the eccentric ring 163, and a tension adjusting spring 165 supported on the pivot shaft 162 for imparting a turning force to the eccentric ring 163 to press the pulley 164 against a belt A.
A hydraulic damper 170 is provided between the engine block 160 and the pulley 164. The damper 170 damps the force applied to the eccentric ring 163 when the ring is pushed by the tensioning belt A through the pulley 164.
The hydraulic damper 170 includes a damper body 171 fixed to the engine block 160 by tightening the bolt 161 and formed with an open-topped cylinder chamber 172 in which is slidably mounted a plunger 173 having at its lower portion a pressure chamber 174 in which is mounted a return spring 175 biasing the plunger 173 to press its tip against a protrusion 176 provided on the eccentric ring 163.
The plunger 173 is formed with a reservoir chamber 177 and a passage 178 through which the reservoir chamber 177 communicates with the pressure chamber 174. A check valve 179 is provided near the bottom end of the passage 178.
When the tension in the belt A increases, the eccentric ring 163 is pushed by the belt A through the pulley 164. This pushing force is damped by hydraulic oil sealed in the pressure chamber 174 of the hydraulic damper 170. While the pushing force is greater than the force of the return spring 175 and the tension adjusting spring 165, hydraulic oil in the pressure chamber 174 is allowed to flow into the reservoir chamber 177 through a gap between the sliding surfaces of the plunger 173 and the cylinder chamber 172 and a radial passage 180 formed in the plunger 173, so that the plunger 173 retracts slowly until the pushing force balances with the force of the return spring 175 and the tension adjusting spring 165.
When the belt A slackens and the eccentric ring 163 pivots under the force of the tension adjusting spring 165, the plunger 173 is pushed upward under the force of the return spring 175. As a result, the pressure in the pressure chamber 174 drops below the pressure in the reservoir chamber 177, so that the passage 178 is opened by the check valve 179. Hydraulic oil in the reservoir chamber 177 thus flows smoothly into the pressure chamber 174 through the passage 178, thus allowing the plunger 173 to move quickly upwardly.
The pulley 164 can thus quickly and smoothly move following change in the belt tension when the belt stretches or slackens.
With this type of hydraulic autotensioner, the eccentric ring 163 is coupled to the hydraulic damper 170 by inserting the bolt 161 extending through the eccentric ring 163 into a bolt hole 181 formed in the damper body 171 and then threading the bolt 163 into the engine block 160. Thus, before the hydraulic autotensioner is mounted on the engine block 160 or after it has been dismounted from the engine block, the eccentric ring 163 might separate from the hydraulic damper 170. This makes it difficult to mount the damper.
An object of this invention is to provide an autotensioner which can prevent separation of its eccentric ring from the hydraulic damper and thus can be mounted easily.